Soil organic carbon–stock changes in Flemish grassland soils from 1990 to 2000

Abstract

Total soil organic-carbon (SOC) stocks for grassland soils in Flanders (N Belgium) were determined for the Kyoto Protocol reference year 1990 and 2000 in order to investigate whether these soils have been CO 2 sinks or sources during that period. The stocks were calculated by means of detailed SOC datasets, which were available at the community scale for the whole of Flanders. The total SOC stocks for Flemish grassland soils (1 m depth) were estimated at 38 Mt SOC in 1990 and 34 Mt SOC in 2000. The loss of SOC resulted from a decrease in the SOC content of grassland soils (71%) and could also partly (29%) be explained by a decline in grassland area. Significant decreases in %SOC for the 0-6 cm depth layer were found for the 1990s for the coarser-textured soils with SOC losses ranging between -0.3% and -0.5% over the 10 y period. Specific management practices that disturb the SOC balance such as conversion to temporary grassland and a reduction of animal-manure application are hypothesized to have contributed to the observed loss of SOC stocks. We furthermore conducted an analysis of uncertainty of the 1990 and 2000 grassland SOC-stocks calculation using Monte Carlo analysis. Probability-distribution functions were determined for each of the inputs of the SOC-stock calculation, enabling us to assess the uncertainty on the 1990 and 2000 SOC stocks. The frequency distributions of these simulated stocks both closely approached lognormal distributions, and their 95%-confidence intervals ranged between 150% and 50% of the calculated mean SOC stock. The standard error on the measured decrease in SOC stocks in Flemish grassland soils during the 1990s was calculated to be 7-8 Tg SOC, which is equivalent to twice this decrease. This clearly shows that large-scale changes in SOC stocks are uncertainty-ridden, even when they are based on detailed datasets.

Changes in carbon stocks of Danish agricultural mineral soils between 1986 and 2009

“…Somewhat smaller estimates have been reported for cropland (90 t C ha −1 ), grassland (118 t C ha −1 ) and forest soils (98 t C ha −1 ) in southeast Germany (Wiesmeier et al , ), mainly because there is less SOC below the top‐soil (A horizon). Meersmans et al () also found less SOC stored in the 0–100‐layer under cropland and grassland in northern Belgium (86 and 108 t C ha −1 , respectively), while another study of North Belgian soils (Mestdagh et al , ) reported SOC storage ranging from 111 to 163 t C ha −1 in grasslands (excluding grasslands on polders and dunes). For Scottish arable soils, Chapman et al () reported SOC stocks of 111 t C ha −1 .…”

Spatial analysis of soil organic carbon evolution in Belgian croplands and grasslands, 1960-2006

“…In the north Belgian grassland soils, Mestdagh et al (2009) estimated a decrease in SOC between 1990. from 38 to 34 Mt) due to a reduction of C input from manure and conversion to temporary grasslands.…”

Stagnating crop yields: An overlooked risk for the carbon balance of agricultural soils?

“…3). In several SOC studies in Europe it was also assumed that a decreased application of farmyard manure resulted in a decreased C supply in cropland soils (Capriel, 2013;Goidts and van Wesemael, 2007;Mestdagh et al, 2009;Sleutel et al, 2007).…”